Treatment of aluminum



- erable extent.

Patented Sept. 11, 1934 UNITED STATES PATENT OFFICE Research Laboratories, Inc.,

Dover, Del., a

corporation of Delaware No Drawing. Application February 6, 1932, Serial No. 591,455

20 Claims. (Cl. 75-58) This invention relates to the treatment of aluminum, and has for its principal object the provision of an improved method of hardening aluminum. More generally, the invention aims to improve the properties of aluminum for various industrial uses, as, for example, in die casting, structural purposes, where a high polish is desired, etc.-

It has long been known that small percentages of copper, up to about 10%, harden aluminum, and alloys of aluminum with such amounts of copper have been industrially used to a consid- Like aluminum itself, however, these aluminum-copper alloys do not polish well, and such polish as may be imparted is maintained for only a short time. The present invention is particularly concerned with this art of hardening and improving the properties of aluminum by the inclusion therein of small amounts of copper. I have discovered, however, that aluminum products of vastly superior properties are attainable when the copper admixed with the aluminum is previously treated with arsenic in the manner hereinafter described.

The present invention accordingly involves the incorporation in molten aluminum of a few percent of arsenious-treated copper. I have found that the inclusion of a fraction of one percent of magnesium in the aluminum, preferably as early in the melting of the aluminum as the molten metal can be stirred, facilitates the treatment process, notably by increasing the fluidity of the molten metal and by lowering the temperature at which the molten meal becomes sufiiciently fluid to pour readily. The arsenioustreated copper is preferably added to the fluid molten metal. The resulting molten metal mixture is maintained at the prevailing temperature with appropriate stirring, for-a sufficient time to secure substantial homogeneity. The optimum advantages of the invention are attained by subjecting the resulting homogeneous molten mixture to the action of a high vacuum. If desired, a small amount of silicon, say 0.5 to 1%, may be included in the molten metal mixture to impart additional hardness to the ultimate aluminum product.

In practicing the invention, a suitable quantity of arsenious-treated copper is first produced, and then added to an appropriately molten mass of aluminum. In preparing the arsenious-treated copper, it is my preferred practice to cut the metal into small lamellas. Such lamellas may be advantageously obtained by cutting sheet copper, say about one-sixteenth inch in thickness, into one-fourth to one-half inch squares. The lamellas are then dipped or immersed in an alkali liquor for a period of from ten to thirty minutes.

The arsenious treatment of the conditioned lamellas is preferably carried out in a glazed or enamelled fire-clay crucible. Alternate thin layers of the lamellas and a compound of arsenic are packed cold in the crucible. The 05 charge is covered with a layer of linseed oil and the crucible hermetically sealed. The crucible is then gradually heated from the bottom up until it approximates a white heat. The charge is then cooled down, preferably in the crucible. The lamellas, now highly porous and of a bluishblack color, adhere slightly to one another but may be readily separated by a slight crushing pressure, crushing by hand being usually adequate. The lamellas will be found at this stage to be impregnated or penetrated with arsenic to the contemplated extent.

Any suitable compound of arsenic may be used in the treatment of the copper. Very satisfactory results are secured with arsenic oxide or an acid (AS203). Arsenic-sulphur compounds give satisfactory results, particularly the natural mineral realgar consisting principally of AszSa. The natural mineral orpiment (AS2S3) may also be used.

In the following description, I give my present preferred procedure for producing the arsenioustreated copper. It is to be understood, however, that this description is illustrative and in no sense limiting or restrictive.

Equal parts by weight of potassium nitrate (or sodium nitrate) and tartaric acid are intimately mixed and ground together in a pebble mill. The resulting mixture is placed in a crucible and heated to a cherry red temperature, say in the neighborhood of 760 C. The crucible may be of steel or other appropriate metal or may be an enameled or glazed fire-clay crucible. Preferably, the comparatively cold crucible is about one-third filled with the mixture and gradually heated to cherry red. In the course of the heating the mixture fuses with the evolution of gas and becomes dark and charred. The crucible is cooled, and its charge, now a blackish ash or cinder, is removed from the crucible, crushed and dissolved in water to form a substantially concentrated lye liquor.

Sheet copper of any suitable thickness is cut into relatively small squares or lamellas, say about 4" squares. These lamellas are subjected to the action of the lye solution, as for example by immersing them in the solution for from 10 to 30 minutes, whereupon the copper is prepared and conditioned for its treatment with arsenic.

A crucible (preferably an enameled or glazed crucible of fire-clay or the like, although a steel or equivalent metal crucible may be used) is arranged to be gradually heated from the bottom up, within a hood or housing for collecting and appropriately disposing of the evolved gases. The bottom of the crucible is covered with a layer, say about A" deep, of an appropriate compound of arsenic, such as arsenic oxide (AS203) or a sulfide of arsenic. The crucible is then charged to about of its depth with alternate layers of the conditioned copper lamellas and the arsenic compound. The lamella layers may be approximately in depth, while the layers of the arsenic compound may be considerably shallower. On top of the uppermost layer (preferably but not necessarily of the sonic compound) is poured a layer of linseed oil sufiicient to completely cover the charge in the crucible. The crucible is covered and hermetically sealed by luting or other appropriate means, and gradually heated, from the bottom up, until it becomes approximately white hot, say in the neighborhood of 950 C. This is preferably accomplished in a period of about 2 hours. In the course of the heating, vapors are evolved and escape through cracks in the crucible cover, and because of their arsenic content these vapors are collected and suitably disposed of.

The crucible and its charge are cooled ,without removing the cover. When cooled, the lamellas will be found to be penetrated with a substantial amount of arsenic and to have maintained their original physical configuration and although porous to be extremely hard. The 'arsenioustreated copper lamellas are now ready for the treatment of aluminum in accordance with the invention.

An appropriate quantity of metallic aluminum is heated in any suitable type of furnace. When the aluminum is sufficiently molten to stir, a small amount of magnesium metal, say about 0.25%, is preferably added and thoroughly incorporated throughout the aluminum by stirring. Usually, the temperature of the aluminum is around 550 C, when sufiiciently molten to stir. At this temperature, the aluminum is in a somewhat doughy and viscous molten state. Heating of the aluminum is continued until it becomes quite fluid, ordinarily at a temperature around 660 C. From 3 to 7% by weight of the arsenious treated copper is then added to the molten aluminum while in a sufliciently fluid state to pour readily. It is my preferred practice to add from 4 to 5% by weight of the arsenious treated copper to the molten aluminum. The molten mixture is stirred to assure homogeneity, and is maintained at the elevated temperature, around 660 C, for from 15 to 20 minutes.

If desired, a small percentage of silicon metal, from 0.5 to 1% by weight, may be added to the molten mixture to increase the hardness of the ultimate aluminum product.

The molten metallic mixture is now subjected to a high vacuum, as nearly perfect as possible, while maintaintained at a temperature in the neighborhood of 660 C. This vacuum treatment may be advantageously carried out in the electric furnaces described in my United States Patents Nos. 1,498,990 and 1,499,317. It is my preferred practice to carry out the melting, mixing and vacuum treatment in the same furnace, but separate furnaces may of course be used. The vacuum furnace should be capable of establishing and maintaining an extremely high vacuum since the quality of the final aluminum product is in large measure dependent upon the efilcacy of the vacuum treatment. While under the vacuum, various impurities, consisting largely of arsenic compounds, are removed from the metal, and may be conveniently absorbed in water or other appropriate liquid. Following the vacuum treatment, the furnace is opened, and the metal cast into ingots or other suitable forms for subsequent fabrication or use.

While certain of the advantages of the invention may be secured by omission of the vacuum. treatment such as increased hardness, the aluminum product resulting from the vacuum treatment possesses such superior properties (particularly with respect to ductility and nonbrittleness) that the vacuum treatment is desirable in practically all cases and is essential if the ultimate aluminum product is to be of the optimum quality. Following the vacuum treatment, the aluminum product, after solidification, is substantially free of arsenic, and the usual analytical methods fail to show any arsenic in the product. The actual percentage of copper 105 in the ultimate aluminum product, as determined by analytical methods, is substantially lower than would be expected by calculation. This. I believe, is due to some combination between aluminum and copper which transmutes a certain amount of the copper to a state undetectable by ordinary analytical methods. Thus, when an amount of arsenious-treated copper has been added to the aluminum to give by calculation 4% of copper in the final aluminum product 115 (which is my preferred practice) it will be found that only about 1 to 3% copper may be reported by actual chemical analysis of the final aluminum product.

The final aluminum product resulting from the 1 0 preferred practice of the invention is hard, tough, ductile and non-brittle. Upon fracturing, it shows a sharp crystalline structure, preceptibly difierent from the coarse and rather fibrous structure of aluminum. The aluminum product 125 of the invention takes and maintains a high polish.

While the arsenious-treated copper is preferably made of copper metal, alloys containing a. substantial quantity of copper, such as brass, bronze etc. may be similarly arsenious-treated, and in some cases may be advantageously used as the arsenious-treated copper in the practice of the invention. The use of such copper alloys introduces into the aluminum a small percentage of such non-cuprous metal or metals as are included in the copper alloy. Where the presence of such non-cuprous metals in the final aluminum product is advantageous or at least not objectionable, the arsenious treated copper for the practice of the invention may be made of such copper alloys.

I claim:

1. The method of treating aluminum which comprises melting a quantity of alumnum and 145 adding thereto a few percent by weight of copper impregnated with; arsenic and stirring to obtain a homogeneous molten mixture.

2. The method of treating aluminum which comprises thoroughly incorporating a fraction 5 of one percent by weight of magnesium metal in molten aluminum, and adding to the resulting molten mixture a few percent by weight of copper impregnated with arsenic.

3. The method of treating aluminum which comprises melting a quantity of aluminum and adding thereto from 3 to 7% by weight of copper impregnated with arsenic and stirring to obtain a homogeneous molten mixture.

4. The method of treating aluminum which comprises thoroughly incorporating about 0.25% by weight of magnesium metal in molten aluminum, and adding to the resulting molten mixture from 3 to 7% by weight of copper impregnated with arsenic.

5. The method of treating aluminum which comprises melting a quantity of aluminum and adding thereto a few percent by weight of copper impregnated with arsenic and stirring to obtain a homogeneous mixture, and subjecting the resulting molten mixture to a high vacuum.

6. The method of treating aluminum which comprises thoroughly incorporating a fraction of one percent by weight of magnesium metal in molten aluminum, adding to the resulting molten mixture a few percent by weight of copper impregnated with arsenic, and subjecting the resulting molten mixture to a high vacuum.

'7. The method of treating aluminum which compises melting a quantity of aluminum and adding thereto from 3 to 7% by weight of copper impregnated with arsenic and stirring to obtain a homogeneous molten mixture, and subjecting the resulting molten mixture to a high vacuum.

8. The method of treating aluminum which comprises thoroughly incorporating about 0.25% by weight of magnesium metal in molten aluminum, adding to the resulting molten mixture from 3 to 7% by weight of copper impregnated with arsenic, and subjecting the resulting molten mixture to a high vacuum.

9. The method of treating aluminum which comprises adding to molten aluminum about 5% by weight of copper impregnated with arsenic, and subjecting the resulting molten mixture to a high vacuum.

10. The method of treating aluminum which comprises adding to molten aluminum a fraction of one percent by weight of magnesium metal and about 5% by weight of copper impregnated with arsenic, and subjecting the resulting molten mixture to a high vacuum.

11. The method of treating aluminum which comprises adding to molten aluminum about 0.25% by weight of magnesium metal and about 5% by weight of copper impregnated with arsenic, and subjecting the resulting molten mixture to a high vacuum.

12. The method of treating aluminum which comprises heating a quantity of aluminum until it becomes sufficiently molten to stir, adding a fraction of one percent by weight of magnesium metal to the molten aluminum, further heating the resulting molten mixture until it becomes sufliciently fluid to pour readily, and adding to the fluid molten mixture a few percent by weight of copper impregnated with arsenic with adequate stirring to produce a homogeneous mixture.

13. The method of treating aluminum which comprises heating a quantity of aluminum until it becomes sufficiently molten to stir, adding a fraction of one percent by weight of magnesium metal to the molten aluminum, further heating the resulting molten mixture until it becomes sufllciently fluid to pour readily, adding to the fluid molten mixture a few percent by weight of copper impregnated with arsenic, and subjecting the resulting fluid molten mixture to a high vacuum.

14. The method of treating aluminum which comprises heating a quantity of aluminum until it becomes sufllciently molten to stir, adding a fraction of one percent by weight of magnesium metal to the molten aluminum, further heating the resulting molten mixture until it becomes sufliciently fluid to pour readily, adding to the fluid molten mixture from 3 to 7% by weight of copper impregnated with arsenic, and subjecting the resulting fluid molten mixture to a high vacuum.

15. The method of treating aluminum which comprises heating a quantity of aluminum until uct resulting from heating a mixture of an alkali nitrate and tartaric acid to a cherry red temperature in the neighborhood of 760 C., heating alternate thin layers of the so-conditioned lamellas and a compound of the group consisting of arsenic combined with sulphur and arsenic combined with oxygen in a closed vessel to a temperature of about 950 C., melting a quantity of aluminum and adding thereto from 3 to 7% by weight of said arsenioustreated copper, and subjecting the resulting molten mixture to a high vacuum.

17. The method of treating aluminum which comprises conditioning a quantity of copper by immersion in a liquor formed by heating a mixture comprising an alkali metal nitrate and tartaric acid to a temperature above the fusing temperature of the mixture and leaching the resulting product with a suitable liquid solvent, heating the so-conditioned copper in the presence of a compound of the group consisting of arsenic combined with sulphur and arsenic combined with oxygen, and melting a quantity of aluminum and adding thereto a few percent by weight of the resulting copper product.

18. The method of treating aluminum which comprises conditioning a quantity of copper by immersion in a liquor formed by heating a mixture comprising an alkali metal nitrate and tartaric acid to a temperature above the fusing temperature of the mixture and leaching the resulting product with a suitable liquid solvent, heating the so-conditioned copper in the presence of a compound of the group consisting of arsenic combined with sulphur and arsenic combined with oxygen, melting a quantity of aluminum and adding thereto a few percent by weight of the resulting copper product, and subjecting the resulting molten mixture to a high vacuum.

19. The method of treating aluminum which comprises conditioning a quantity of copper by immersion in a liquor formed by heating a mixture comprising an alkali metal nitrate and tartaric acid to a temperature above the fusing temperature of the mixture and leaching the 7 resulting product with a suitable liquid solvent,

heating the so-conditioned copper in the presence of a compound of the group consisting of arsenic combined with sulphur and arsenic combined with oxygen, melting a quantity of aluminum and adding thereto about 3% to 7% by' weight of the resulting copper product; and subjecting the resulting molten mixture to a high vacuum.

20. The method of treating aluminum which comprises conditioning a quantity of copper by immersion in a liquor formed by heating a mixture comprising an alkali metal nitrate and tarcent by weight of magnesium metal, further heating the resulting molten mixture and adding thereto about 3% to 7% by weight of the arsenic treated copper, and. subjecting the resulting molten mixture to a high vacuum.

ROBERT BEYER. 

